Stroke control means for hydraulic pumps and motors



SCP- 4, 1951 R. F. HoRToN 2,566,418

Y STROKE CONTROL MEANS FOR HYDRAULIC PUMPS AND MOTORS Filed June 10, 1947 2 VSheetfS--Sheet l R. F. HORTON Sept. 4, 1951 STROKE NTROL MEANS FOR HYDRAULC PUMPS AND MOTORS Filed June l0, 1947 2 Sheets-Sheet 2 ATTORIIEY Patented Sept. 4, 1951 assaut;

STROKE CONTROL MEANS FOR HYDRAULIC PUMPS AND MOTORS Roger F. Horton, Hempstead, N. Y., assignor, by

mesne assignments, to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application June 10, 1947, Serial No. 753,7 t

11 claims. l

'I'his invention relates to apparatus for co in the high pressure side of the fluid circuit or system in which the device is employed. Such regulation of the stroke of hydraulic pumps and motors is unsatisfactory because the stroke is varied from maximum to zero in direct proportion to increase in the pressure in the system and thus cannot develop the horsepower of which the system is capable. As pressure increases the track ring is moved proportionately in a. direction from full stroke position to zero stroke position and the horsepower delivered by a pump or developed by a motor, is limited and held constant -because the volume of iluid displaced decreases as the pressure increases.

It is an object of this invention to provide stroke control means not subject to the above stated disadvantage.

Another object of the invention is to provide a simple, practical, and efn'cient device for controlling the stroke of hydraulic pumps and motors which is not operative to decrease the stroke until the pressure in the system exceeds a given amount. Another object of the invention is to provide strike control means for an hydraulic power conversion unit which will not become operative to modify or limit the stroke until a critical pressure is reached and which will then serve to gradually decrease the iiow by reducing the stroke without necessarily decreasing or limiting the speed of rotation of the unit.

Another object of the invention is to provide a rotary power conversion unit, of the type employing a track ring to control the length of the stroke of the pistons, including a member movable in a plurality of directions in response to increase in fluid pressure in the system comprising said unit, in combination with means for absorbing energy of the movement of said member in one direction up to a given amount thereby causing said means to move in the other direction above said given pressure thereby swinging the track ring to decrease its eccentricity and progressively limit the stroke of the pistons in 'response to increase in pressure above said given amount.

Another object of the invention is to provide an hydraulic rotary pump in which the volume 4herein;

. 2 of fluid displaced per revolution remains constant up to a critical pressure and then decreases without substantially lowering the critical pressure throughout a. range of. movement from maximum stroke position to zero stroke position.

Another object of the invention is to provide automatic control means adapted to prevent overloading of the driven member in an hydraulic pump circuit, as well as overloading of the hydraulic motor itself, without 'limiting the flexibility of the pressure-:dow relationship up to a maximum horsepower.

Another object of the invention is to provide pressure regulation means for an hydraulic motor which will permit the motor to develop a continuously increasing horsepower up to a given or critical pressure and then gradually decrease the stroke and the torque developed without speed change.

Other objects of the invention will be in part obvious or in part pointed out hereinafter- The invention accordingly consists: in the icatures of construction, combinations of elements. arrangements of parts, and in the several steps and relation and order of each oisaid steps t0 one or more of the others thereof, all as will be pointed out in the following description, and the scope of the application of which will be indicated in the following claims.

The invention will best be understood l1' the following description is read in connection with the drawings, in which,

Figure 1 is a cross sectional view of a device embodying my invention, and which may be employed as a pump or motor equipped with apparatus embodying my invention in a position before critical pressure has been reached;

Figure 2 is a front elevational view of the device shown in Figure 1, partly cut away and partly in cross section;

Figure 3 is a diagrammatic view showing the change in position of the pressure control means after critical pressure has been reached;

Figure 4 is a view similar to Figure 2 o1' another embodiment of the invention;

Figure 5 is a schematic view of an hydraulic circuit employing an hydraulic pump equipped with the pressure regulator means disclosed Figure 6 is a schematic view of an hydraulic circuit employing an hydraulic motor equipped with the pressure regulator means disclosed herein; and Y Figure 7 is a detail cross sectional view taken on the line 1-1 of Figure 3.

In the drawings the numeral lll indicates the casing or shell of an hydraulic pump orl motor.l Pivotally .mountedwithin the casing on the lball pivot I2 is a track ring assembly comprising the outer track I4, and the inner track I6, separated from the outer track by the race or bearings I8.

Within the inner track I6 is the pintle 20 in which are the fluid conduits 22 and 24 which communicate through the branch passages 22* and 24a respectively with the grooves 23 and 25 respectively-in the peripheral surface of the pintle. Surrounding the pintle 20 is a bearing ring 26 having the ports 28 therein at spaced intervals, and surrounding the bearing ring 26 is the rotor 30 having the cylinders 3l communieating with the ports 28 respectively. In the cylinders are the pistons 32 respectively which project from the cylinders and the outer ends of which rest against the inner surface of the inner track I6.

The axes of the rotor and of the track ring as sembly are parallel. The center of the rotor is at 34. l In the position of the track ring assembly as shown in Figure 1 its axis is at 36. The center of the track ring of course shifts as the track ring assembly swings onA pivot I2 and this movement controls the stroke of the pistons, changing the stroke from maximum in the eccentric position of the track ring in relation to the rotor center shown in Figure 1 to zero stroke when the axes of the track ring and rotor coincide. As shown in Figure 1 the track ring as- -fitted into the discharge end of portion 80 of conduit 8U.

Spring 50 is designed so that it will be compressed by less force than is required to swing the -track ring on its pivot and so increase in the pressure in the system acting in the bore 62 of cylinder 60 will iirst cause arm 48 to rotate in a clockwise direction on its pivot thus moving cylinder 60 away from piston 66 which movement is absorbed in compressing spring 50 until the cupshaped end 48 of portion 44 of arm 40 comes into contact with the annular flange 58 on the head of the adjustable screw member 54. When arm sembly is in its extreme position to the right in Figure 1 as viewed by the reader, and abuts against the stop 38 carried by the pivoted arm 40 which forms part of the pressure control apparatus which will now be described.

The arm 4 8 is pivoted to the casing on pivot member 42 projecting inwardly from the casing wall and made hollow to provide a-fluid passage as will be described. Behind the pivot 42 the arm comprises an elongated portion 44, the rear end 46 of which is turned inwardly substantially at a right angle and is cup shaped providing a space 48 adapted to receive one end of a coil spring member 50. The other endof spring 50 abuts against the inner surface of the cup-shaped flange 52 at the inner end of the adjustable screw member 54 which extends through the casing wall, and axially through the said space 48 of the arm portion 44, and said coil spring member 50, the head 55 of which is received in the recess 56 in the outer face of the casing.

' The front end portion 68 of arm 46, through which pivot 42 extends, is inclined at an oblique angle with respect to the said rear portion 44, and

constitutes a cylinder having the bore 62 extending axially from its inner end in which is received the inner end 64 of -the piston 66. The

outer end of piston 66 projects from bore 62 and space beyond the inner end of piston 66, from the '(0 high pressure side of the fluid circuit in which the pump or motor is incorporated, through the opening 'I8 extending through the casing, the conduit the inner portion 80* of which is 40 cannot swing further in a clockwise direction. becausey of end 48 of arm portion 44 coming into contact with ange 58 of member 54, see Figure 3, further increase in the fluid pressure will cause piston 66 to move outwardly in cylinder 60 thus exerting a thrust against link 10, causing it to rotate counter-clockwise and moving pivot 68 outwardly. A thrust is thus exerted against the track ring assembly tending to rotate it on its pivot vI2 in a counter-clockwise direction, from full stroke toward no stroke position, against the spring which is interposed between the casing and the track ring on the opposite side of pivot I2 from lug 14. Spring 90 is made strong enough to bias the track ring to full stroke position until the fluid pressure rises sufliciently to cause an opposing thrust to be exerted through link 'I0 as has been described. Due to the angular relation between link 'I0 and piston 66 a side load or reaction load will be imposedl on the linkage during movement of the track ring toward zero stroke position. 'I'his side load will obviously be taken up by the walls of the cylinder 60. When the pressure rises above the predetermined critical amount the resistance of spring 90 is overcome progressively until the center of the track ring coircides with the center of the rotor which is the no stroke position. In this position the device if employed as a pump will not be operative to deliver, any propulsion fluid but its rotor may continue to rotate and its rate of rotation may under certain circumstances increase. In this no stroke position if the device is employed as a motor, rotation of the rotor Will cease and no fluid will' flow through the device.

.When the system pressure falls below the critical amount the force of the fluid pressure 'will again be fully absorbed by spring 50 and spring 90 will swing the track ring assembly on its pivot I2 in a clockwise direction all the way to maximum stroke position thus again making available the full horsepower of which the device is capable.

The ball bearing I2 on which the track ring assembly pivots is supported in the V-shaped groove 92 provided in the inner end of an adjustable screw member 94 extending through the casing wall with its head 96 received in the recess 98 in the outer surface of the casing. The shank of this screw may be reduced in diameter as at |00 (Fig. 2) and a packing ring IUI inserted around the shank in the resulting space to provide a iiuid seal. The outer surface of the outer track ring I4 is grooved at |02 to receive and provide a cage engaging ball pivot I2. The track ring is prevented from being dislodged aligned and communicates with the hollow pivot 76 from its pivot` by adjustable Stop 'means Which as shown is the adjustable screw member |04 which extends through the casing wall opposite screw member 84. Member |04 is adjusted so that its inner end extends beyond the inner surface of the casing wall and approaches sufliciently close to the track ring to insure that the track ring cannot at any time get off or be dislodged from ball pivot I2.

An opening 10 and a conduit 80H, similar to opening 18 and conduit 80 respectively are provided in the casing wall opposite to opening 10 and conduit 80 respectively, and a recess 56a is provided in the casing wall (and closed by a removable screw 51), opposite recess 56 so that the pressure regulating means described herein may be attached at the opposite side of the device, as shown in dotted lines in Figure 1, for use if opposite hand rotation of the rotor is desired. Similarly a boss 9 Ia may be provided on the inner surface of the casing opposite to the boss 9| to facilitate interposing spring 90 between the track ring and the casing on the right hand side of the device as viewed in Figure 1 if the pressure regulating means described herein are transferred to the left hand side of the device as viewed in Figure 1.

In Figures 5 and 6 hydraulic pump and motor systems respectively are shown diagrammatically. In the pump system shown in Figure 5 propulsion fluid is supplied to the pump from the reservoir through conduit I I0, and is supplied from the pump to work through the conduit I2 which has therein the one way iiow or check valve ||4. From the work the spent fluid is returned to reservoir through conduit 20. The uid is received by the pump at low pressure and is discharged through conduit ||2 at high pressure and so a supply of propulsion uid to operate the pressure control means described herein is obtained through conduit |I6 leading from conduit ||2 to the opening 18.

The motor system shown in Figure 6 is similar to the pump system shown in Figure 5 except that the direction of ow is reversed. The propulsion fluid is led from reservoir to the pump p through conduit |20 and from pump p to the motor through conduit ||2, and the spent fluid is returned from the motor to reservoir through conduit H0. The supply of fluid for operating the control means described herein is obtained through conduit IIB leading from high pressure conduit i I2 to' the opening 18.

' As seen in Fig. 6 a relief valve |24 is provided between the pump inlet line |20 and the pump discharge line I|2 `so as to prevent an unlimited build up of pressure in the line I I2 and the motor when the stroke of the pistons in the motor approaches zero. Similarly a flow control by-pass |26 is provided across the pump inlet and outlet lines |20, I|2 to by-pass some of the pump outlet flow not required by the motor at any instant. The by-pass |26 then also serves to prevent the locking of high pressure between the pump discharge and motor inlet when the system is stopped or at any time.

In Figure 4 is shown a modification of the stroke control means described above. In this embodiment the rotor assembly |40, indicated in dotted lines, is contained within a track ring assembly |42 which is mounted within casing |44 on pivot |46. Between the track ring and the casing, linkage is provided comprising a cylinder |48 pivoted to the casing at |50 having therein the piston |52 the outer end of which is connected by pivot |54-to the link |56 which is connected to the track ring by pivot |58. Fluid from the high pressure side of the pump or motor system is supplied to cylinder |48 through flexible conduit |60 extending through the casing. As the lfluid pressure increases in cylinder `by spring |62 which is interposed between the cylinder |40 and the casing wall one end being received in the hollow boss |40 integral with cylinder |46 and the other end being received in a hollow boss |63 on the inner surface of the casing, until the critical pressure is reached. After the critical pressure is reached further outward movement of piston |52 is translated into swingingmovement of the track ring on its said pivot |46 causing it to swing in a counterclockwise direction, as vievfed in Figure 4, against the resistance of spring 64, which is strong enough to`originally bias the track ring to the full stroke position but not strong enough to resist the torque exerted through link |56 after the critical pressure has been reached. A stop member IE6 is provided in the casing wall opposite spring |64 for limiting clockwise swinging movement of the track ring assembly and determining its maximum stroke position. It will be understood that the control means shown more or less diagrammatically in Figure 4, like the control means shown in Figures 1-3 will not affect any change in the position of the track ring until the critical pressure is reached, after which it will gradually reduce the stroke from maximum to zero, in direct proportion to the increase in fluid pressure above the critical amount.

It is desirable to control an hydraulic pump so that it will deliver as much fluid per unit of time at as high a pressure as the system will safely take, thereby obtaining the largest possible horsepower, and to avoid having the stroke decreased as the pressure in the system goes up but while it is still within a safe pressure range, thus causing the amount of duid delivered to decrease, and thereby reducing the horsepower which can be developed. In other words it is desirable to have the volume of displaced uid per revolution of the pump remain constant up to a critical pressure and then have output decrease while holding the critical pressure approximately constant even to zero uid output.

In a motor it is desirable to have an automatic control which prevents overloading ofthe driven member as well as of the motor itself without limiting the flexibility of the pressureflow relationship up to a maximum horsepower.

When pressure control means ofthe kind described herein is applied to a pump it permits'the pump to deliver a maximum of fluid until the critical pressure of the device is reached whereupon the stroke will be gradually reduced.

When the pressure control means described herein is used as a motor it permits increase in horsepower output until the critical pressure for the device is reached after which the stroke cf themotor will be gradually reduced.

It will thus be seen that there has been provided by tlis invention a method and apparatus in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embcdiments might be made of the mechanical features of the above invention and as the art herein described might be varied in variandere ous parts, all without departing from the scope of the invention, it is to be understood that al1 matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

What I claim is:

l. In a power translating device comprising,.a

casing. a rotor within said casing having a number of radial cylinders, and pistons projecting from the ends of said cylinders, hearings carrying said rotor for rotation about a xed axis, a drive shaft extending into said casing and coupled to said roten-and a track ring pivotedly mounted within said casing in controlling engagement with theouter ends of saidV pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor, iluid inlet and outlet passages extending through said casing and communicating with said cylinders, and means operative above a critical pressure for swinging the track ringen its said pivot and thereby varying thestroke of the said pistons in said cylinders comprising, linkage interconnected between the casing and the track ring and including a plurality of angularly related members one of which comprises, a portion extensible 8 drive shaft extending into said casing and coupled to said rotor, and a track ring pivotedly mounted within said casing in controlling engagement with the outer ends of said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor, liquid inlet and outlet passages extendingl said pistons in said cylinders comprising, linkwhen subjected to a pressure above a given presl sure, a fluid conduit interconnecting said portion and the high pressure side of said device, and means connected to said angularly related means adapted to absorb the energy imparted thereto by extension of said linkage up to a lgiven amount.

2. In a power translating device comprising, a casing, a rotor within said casing having a number of radial cylinders, and pistons projecting from the ends of said cylinders, bearings carrying said rotor for rotation about a 'xed axis, a drive shaft extending into said casing and coupled to said rotor and a track ring pivotedly mounted within said casing in controlling engagement with the outer ends of said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor, liquid inlet and outlet passages extending through said casing and communicating with said cylinders and adapted to serve alternatively as high pressure orl low pressure conduits respectively according to whether the device is used as a pump or a motor, means operative abovel a critical pressure for swinging the track vring on its said pivot and thereby varying the stroke of the said pistons in said cylinders comprising, linkage interconnected between the casing and the track ring including a portion extensible when subjected to a pressure above a given pressure, tending as it is extended by pressure above said given pressure to swing the track ring in a direction from maximum stroke position to no stroke position, a liquid conduit interconnecting said portion and the high pressure side of said device, and means interposed between the casing and the track ring, on the opposite side of the track ring pivot from said linkage, opposing movement of the track ring induced by the extension of said extensible portion of said linkage and tending to swing the track ring in the direction from no stroke position to maximum stroke position.

3. In a power translating device comprising a casing, a rotor within said casing having a number of radial cylinders and pistons projecting from the ends of said cylinders, bearings carrying said rotor for rotation about a xed axis, a

age interconnected between the casing and the track ring including a portion extensible when subjected toa pressure above a given pressure, and a liquid conduit interconnecting said portion and the high pressure side of said device, meansA interposed between the casing and the track ring on the opposite side of the track ring pivot from said linkage opposing movement of the track ring induced b`y the extension of said extensible portion of said linkage and tending to swing the track ring in a direction from no stroke position to maximum stroke position, and a stop member extending inwardly from the casing toward the track ring opposite the said track ring pivot.

4. In a power translating device comprising a casing, a rotor within said casing having a piurality of radial cylinders and pistons projecting from the ends of said cylinders, bearings carrying saidrotor for rotation about a xed axis, 'a drive shaft extending into said casing and coupled to said rotor, and a track ring pivotedly mounted within said casing in controlling engagement with the outer ends of said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor,

liquid inlet and outlet passages extending through said vcasing and communicating with said cylinders, means operative above a critical pressure for swinging the track ring on its said by reduce the stroke of the said pistons in saidV cylinders comprising, linkage interconnected between the casing and the track ring including a. portion extensible when subjected to a pressure above a given pressure, a iluid conduit interconnecting said portion and the high pressure side of said device, a spring interposed between the casing and the track ring on the opposite side of the track ring pivot from said linkage tending to swing the track ring in a direction to move its axis away from concentricity with the axis of said rotor, the pivot for the track ring comprising a ball and-means for positioning the ball in the casing, the outer face of said track ring being provided with a concavity to t over said ball pivot, and stop means projecting from the casing wall and adapted to prevent the track ring from being displaced from its said pivot. k 5. In a power translating device comprising, a

casing, a rotor within said casing having a number of substantially radial cylinders therein and pistons projecting fromthe ends of said cylinders, bearings carrying said rotor for rotation about a iixed axis, a drive shaft extending into said casing and coupled to said rotor, and a track ring pivotedly mounted within said casing in 9 controlling engagement with the outer ends of said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor and removable from concentricity to eccentricity therewith. liquid inlet and outlet passages extending through said casing and communicating with said cylinders and adapted to serve alternatively as high pressure or low pressure conduits according to whether the device is used as a pump or a motor, means operative above a critical pressure for swinging the track ring on its said pivotto thereby vary the stroke of the said pistons in said cylinders comprising, linkage interconnected between -the casing and the track ring including a portion extensible'when subjected to a pressure above a given pressure, a liquid conduit interconnecting said portion of the high pressure side of said device, means interposed between the casing and the track ring on thaopposite side o! the track ring pivot from said linkage tending to swing the track ring in the direction from no stroke position to maximum stroke position. the said pivot for the track ring comprising a ball, an adjustable screw extending through the Wall oi the casing and having a concavity in its inner end adapted to receive and provide a seat for said bail, the outer surface oi' said track ring including a concave portion which rests on said ball. and an adjusting screw extending through the casing wall and projecting'toward the track ring to prevent said track ring from being unseated from said ball pivot.

6. In a power translating device comprising, a casing, a rotor within said casing having a num ber of radial cylinders and pistons projecting from the ends of said cylinders, bearings carrying said rotor for rotation about a fixed axis, a drive shaft extending into said casing and coupled to said rotor. and a track ring pivotedly mounted within said casing in controlling engagement with the outer ends of said pistons i'or determining ing said rotor for rotation about va iixed the position of said pistons in said cylindermthe axis oi rotation of said track ring being parallel to the axis of rotation of said rotor, liquid inlet and outlet passages extending through said casing and communicating' with said cylinders. means operative above a critical pressure for swinging the track ring on its said pivot to vary the stroke of the said pistons in said cylinders from maximum stroke toward zero stroke comprising, linkage interconnected between the casing and the track ring including a portion extensible when subjected to a pressure above a given pressure, a liquid conduit interconnecting said portion and the high pressure side of said device said linkage comprising. an arm pivotally mounted to the casing intermediate its ends one end of .said arm comprising a cylinder, a piston in said cylinder projecting from the outer end of said cylinder, and a link interconnected between the outer end of said piston and the track ring, said `link and piston together forming a toggie-like connection adapted as said piston moves out oi its said cylinder to break and form a sharper angle, a conduit leading from the high pressure side of the device into the cylinder beyond the inner end of the said piston, a stop member adjacent the other end oi' said pivoted arm, and yielding means interposed between the said other end of said arm and said stop member adapted to offer less resistance to the pressure introduced into said cylinder than is required to move the piston in said cylinder to initiate move- It)v ment of the track ring. and other resilient means pressing against the track ring in a direction tending to resist movement of said piston ,in said piston cylinder in a direction whereby when liquid under-` pressure is introduced into the said cylinder in said arm the arm will ilrst rotate against said rst mentioned resilient means until further rotation is stopped by contact with said stop member whereupon said piston`will move out of itsl said chamber in said arm and in so doing will cause said track ring to. swing in a direction opposed by said second resilient member.

7. In a power translating device comprising, a casing, a rotor within said casing having a num-#- ber of 'radial cylinders, and pistons projecting from the ends of said cylinders. bearings carryaxis.- a drive shaft extending into said casing and coul pled to said rotor. and a track ring pivotedly mounted within said casing in controlling engagement with the outer ends oi' said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track ring beingparallel to the axis of rotation of said rotor, uid inlet and outlet passages extending through said casing and communicating with said cylinders, linkage` including a member variable in length in response to change in pressure interconnected between the track ring and the casing. a connection between said fluid passages and said member. and means rendering said linkage means inoperative to swing the track ring on its; pivot until the iiuid pressure exerted on said member exceeds a predetermined amount.

8. In a power translating device comprising, a casing. a rotor within said casing having a num-- ber -of radial cylinders and pistons projecting from the ends of said cylinders, bearings carrying said rotor for rotation about a, fixed axis, a drive shaft extending into said casing and coupled to said rotor, and a track ring pivotedly mounted Y within said casing in controlling engagement with the outer ends of said pistons for determining the position of said pistons in said cylinders. the axis of rotation of said track ring being parallel to the axis of rotation of said rotor, liquid inlet and outlet passages extending through said casing and communicating with said cylinders and adapted to serve alternatively as high pressure or low pressure conduits' respectively according to whether the device is used as a pump' or a motor, means operative above a critical pressure for swinging the track ring on its said pivot and thereby varying the stroke of the said pistons in said cylinders comprising linkage interconnected between the. casing and the track ring including a member variable in length in response to change in pressure and a link pivotally joined to said member between it and the track ring, means rendering said member sensible to change in pressure in the system, said link and said member being disposed so that'the axis of the link and the axis of said member dcne an :angle variable in response to movement of said member, and yielding means interposed between said linkage and the casing adapted to absorb the energy of movement of said linkage up to a given amount.

9. In a power translating device comprising. a casing, a rotor within said casing having a number of radial cylinders and pistons projecting from the ends of said cylinders, bearings: carrying said rotor for rotation about a iixed axis. a drive shaft extending into said casing and coupled to said rotor and a track ring pivotedly mounted within said casingv in controlling en' sagement with the outer ends of said pistons for Y determining the .position of said pistons in said cylinders, the axis of rotation of said track ring being parallel to the axis of rotation of said rotor, liquid inlet and outlet passages extending 'through said 'casing and communicating with andere means for delaying the movement of said ring andabsorbing the energy ot movement of the track ring comprising a member variable in length in response to change in pressure and a link pivotally joined to said member between it and the track ring, means rendering said member sensible to change in pressure in the system.` 20

said link and saidvi'nember' being disposed so that the axis of the link and the axis of "said member deiine an angle variable in response to movement of said member, and yielding 'means interposed between said linkage and the casing adapted to absorb up to a given, amount of energy of said linkage in moving in response to change in length of.. said memberwhereby no energy is transmitted to the track ring to swing it until said member is `actuated by pressure in excess of said given amount after which the track ring is moved in proportion to increase in pressure above said given amount;

"10. Ina power translating device comprising.

-a casing. a rotor within said casing having a number of radial cylinders. and pistons projecting from the ends of said cylinders, bearings car- 'rying said rotor for' rotation about a fixed axis; a drive shaft extending into. said casing and cylinders, the axis of rotation of said track .ring

about its pivot being parallel to the axis of rotation of said rotor, fluid inlet and outlet passages extending througfh said casing and communicating with said cylinders. actuating means engaging said ring for moving the track ring on its said actuating means induced by increase in pressure of said duid up to a predetermined amount.4

l1. In a power translating device comprising, a casing, a rotor within said casing having a number of radial cylinders. and pistons projecting from the ends of said cylinders, bearings carrying said rotor for rotation about 'a fixed axis.

a drive shaftextending intosaid casing and .coupldto said rotor. and. a track ring pivotally mounted within saidcasing in controlling e11- gagement with the outer ends of said pistons for determining the position of said pistons in said cylinders, the axis of rotation of said track-ring being parallel to the axis of rotation of said rotor, fluid inlet 'and outlet passages extending through said casing and communicating with said cylinders, means operative above a critical pressure for swinging the' track ring on its pivot and thereby varying the stroke of said pistons in said cylinders comprising linkage interconnested between the casing and the track ring I including a member variable in length in respouse to change in pressure and a link pivotally joined to said member between it and the track ring, and means rendering said member sensitive to change in pressure in the system, said link and said member being disposed so that the longitudinal axis of said link and the axis of said' member denne an angle variable in response to variation in length of said member. v

- I ROGER F. 'HORTON REFERENCES CITED The following references are of record in the file1 of this patent:

UNITED STATES PATENTS Number Name Date 2,186,556 Robbins v Jada 1940 45 2,292,191 Tucker Aug. 4, 1942 2,293,692 Wylie A ug. 1s, 1942 2,376,019. sehnen May 15,1945 2,396,459

pivot from maximum stroke to zero stroke, said 50 Bautzenroeder ----1- Oct. 2, 1.945 

